746 
DE. W. B. CARPENTER AND MR. H. B. BRADY ON 
37. The septa, which divide the space enclosed by the spiral lamina into chambers, are 
directly connected with the labyrinthic system, and form a part of the accessory skeleton. 
There is no continuation of the primary lamina as an imperforate facing to them, nor 
is there any analogous investing organ. The septa are therefore entirely secondary, 
and are merely extensions of the labyrinthic system, at regular intervals ; taking a very 
oblique direction, and terminating on the outer surface of the preceding whorl. The 
end of the shell, where, from the greater depth of the layers, and the gradual thinning 
out of the chambers, the septa form a prominent feature, shows most clearly their can- 
cellated structure and the sort of connexion that exists amongst them. A magnified 
drawing of this region (Plate LXXIX. fig. 3) bears a strong general resemblance to those 
portions of ParJceria in which the ‘radial tubes’ are largely developed, though differing 
in several essential characters. Not only are the cancellated structures of the septa 
connected, but there is free communication between the adjacent chambers of the same 
layer. In other words, whilst the spiral lamina is imperforate, the septa have numerous 
perforations which allow the passage of sarcode-stolons. 
38. But neither the cancellated structure immediately lining the primary lamina, nor 
its septal developments, can be distinguished in any very definite manner from further 
ingrowths of subordinate importance, which to a greater or less extent occupy the inte- 
rior of the chambers. These 4 tertiary ’ extensions are of very irregular contour ; and 
being usually built up of the coarsest particles, are less easily made out. 
39. Thus whilst the 4 primary skeleton,’ or what may be regarded as such, is simple and 
easily understood, the accessory structures are of somewhat complex character, and 
present appearances very diverse in different specimens, not only from the variable extent 
to which they are developed, but also in their disposition and texture. Some specimens 
show scarcely any traces of the accessory skeleton, beyond that already indicated as 
lining the spiral lamina and forming the septa ; whilst there are others in which the 
sarcode-cavities are to a great degree filled up by its extension into their interior ; but 
in either case some portions of the superadded structure in each chamber are prolonged, 
until they rest upon its floor. In those specimens which have their cavities least filled 
up, the ingrowths take the form of tubular columns, which traverse the chambers in a 
radial direction (i. e. perpendicular to the spiral lamina), terminating either on the 
septum of the previous chamber, or on the exterior wall of the preceding whorl of 
chambers. In others they are more massive and irregular, and appear to be arranged 
so as to subdivide the chambers in an incomplete manner into chamberlets. When this 
latter condition exists, the intersection of the chambers does not take place at regular 
intervals ; but the wide central portion of each is left comparatively open, and the 
ingrowths increase in frequency as the sides thin out. Transverse sections of the larger 
specimens present to the naked eye an appearance as of dark spots set at very regular 
intervals along the spiral band, which on examination are found to indicate the central 
larger chamberlets in the successive chambers; that is, the wider portions have the 
fewest intersecting shelly growths. The smaller chamberlets at each side are hardly to 
